Compared with silicon (Si), silicon carbide (SiC) has characteristics in which a band gap is larger and a dielectric breakdown electric field is higher in an order of magnitude. Therefore, silicon carbide is expected as a material used for a power device. Particularly, a Schottky diode of a unipolar type rectifying device which is operated only by majority carriers is an effective technology for reducing loss of a power module because electric current in the reverse direction (recovery current) at the time of switching operation is not flown due to device constitution.
The Schottky diode obtains rectification by using a Schottky barrier which is generated by difference between a work function of a metal and electron affinity of a semiconductor. Leakage current in the reverse direction can be reduced by using a metal material having a high Schottky barrier height at a Schottky junction part. In this case, however, built-in potential at the time of forward bias becomes higher. The built-in potential at the time of the forward bias can be reduced by using a metal material having a low Schottky barrier height at the Schottky junction part. In this case, however, the leakage current in the reverse direction becomes higher.
With respect to the Schottky diode described above, a structure referred to as a junction barrier Schottky diode (hereinafter, referred to as a “JBS diode”) in which a plurality of junction barriers are provided at the Schottky interface is proposed as a structure for suppressing the leakage current in the reverse direction by reducing an electric field applied to an interface between a metal film and a semiconductor film (hereinafter, referred to as a “Schottky interface”) at the time of application of voltage in the reverse direction. The JBS diode can reduce the electric field at the Schottky interface because a depletion layer extends from the junction barrier part at the time of application of voltage in the reverse direction.
As a structure for suppressing resistance increase at the time of an operation in the forward direction in the JBS diode, a structure increasing an impurity concentration in a region surrounded by the junction barrier is disclosed in Japanese Unexamined Patent Application Publication No. 2003-188391.